1. Field of the Invention
The present invention relates to an image information recording/reading method and apparatus for storing recording light carrying image information as an electrostatic latent image on an image detector that converts the recording light into electric charges that represent a latent image for storage, and reading out the electrostatic latent image stored in the image detector.
2. Description of the Related Art
Conventionally, systems that use an image detector, such as a facsimile machine, copying machine, and radiation image obtaining system have been known.
For example, in medical X-ray and other radiography, a system that uses an image detector having an X-ray sensitive photoconductor made of, for example, a-Se (amorphous selenium) plate to reduce the radiation dosage received by a subject, and to improve the diagnostic capability has been known. The system irradiates recording light, such as X-rays carrying image information on the image detector to store electric charges that represent a latent image of the image information into a storage section of the detector, and thereafter reads out the electrostatic latent image carried by the charges representing the latent image, i.e., the image information stored in the image detector by scanning the image detector with a reading electromagnetic wave, such as a laser beam (hereinafter referred to as “reading light”), and detecting the electric current generated in the image detector by the scanning through flat or comb electrodes on both sides of the detector.
The process for recording image information on the image detector, and reading out the recorded image information from the image detector differs from system to system, depending on the layer structure of the image detector used. For example, when an image detector having electrodes on both sides, with a recording and reading photoconductive layers disposed therebetween is used, the recording light is irradiated on the recording photoconductive layer to form an electrostatic latent image in the storage section of the image detector with a recording voltage being applied between the electrodes, and thereafter the electrodes are short-circuited to be maintained at the same potential, then the reading photoconductive layer is scanned with reading light through the electrode having transparency to the reading light (hereinafter referred to as “reading side electrode”), and the electric current generated by the photoinduced discharges of electron/hole pairs (charge pairs) produced at the interface between the reading side electrode and reading photoconductive layer is converted into a voltage signal to electrically read out the electrostatic latent image. In this case, the section of the detector that has received no recording light generates no electric current, and the section that has received higher intensity reading light produces a larger amount of electric current at the time of reading the electrostatic latent image. The system that reads out the electrostatic latent image with the electrodes being short-circuited after recording as in the system described above is referred to as the short-circuited reading system, and the system in which a larger amount of electric current is generated at the brighter section of the image is referred to as the positive system.
One example of a specific layer structure of the image detector used for the short-circuited reading and positive system comprises a first electroconductive layer (hereinafter referred to as the “recording side electrode layer”); a recording photoconductive layer; a trap layer as the storage section; a reading photoconductive layer; and a second electroconductive layer (hereinafter referred to as the “reading side electrode layer”) as described, for example, in U.S. Pat. No. 4,535,468.
Also, there has been proposed an image detector, as one of the positive type image detectors, comprising a first electroconductive layer having transparency to recording radiation; a recording photoconductive layer that takes on photoconductivity when irradiated with the recording radiation; a charge transport layer that serves substantially as an insulator against the charges having the same polarity as that of the charges charged on the first electroconductive layer, and serves substantially as an electrical conductor for the charges having the reverse polarity; a reading photoconductive layer that takes on photoconductivity when irradiated with reading light; and a second electroconductive layer having transparency to reading light, layered in this order, and having a storage section at the interface between the recording photoconductive layer and charge transport layer as described, for example, in U.S. Pat. No. 6,268,614 and Japanese Unexamined Patent Publication No. 2000-284056.
Here, in the short-circuited reading system, a discharge current continues to flow for about one second just after the electrodes on both sides are short-circuited. If an electrostatic latent image is read out during this time period, the quality of the image is degraded, because the discharge current is added to the signal current. Accordingly, it is necessary to read out the image after about one second or more has elapsed from the time when the electrodes are short-circuited in order to obtain a high quality image, and it is difficult to use the conventional short-circuited reading system for obtaining a moving-picture-like image, in which a plurality of image frames needs to be obtained within one second, so that its use is limited to still picture imaging.
In the mean time, there is a demand for a system that allows the user to set the optimum conditions for still picture imaging, including positioning, confirmation of an imaging timing and sensitivity requirements by moving picture imaging prior to the still picture imaging, and immediately thereafter obtain a still picture under the optimum conditions. In this case, it is preferable that the same image detector is to be used for both motion picture imaging and still picture imaging to eliminate a switching time loss.
The use of the conventional short-circuited reading system is limited to the still picture imaging as described above, so that it can not respond to such a demand.
For this reason, there has been proposed an image information recording/reading method and apparatus capable of imaging moving pictures for use with the positive and short-circuited reading system as described in Japanese Unexamined Patent Publication No. 2001-119626.